System for transmitting sound-carrying and field currents to remotely located dynamic loud speakers



Sept. 13, 1932. L. o. PAINTER ET AL 1,377,034

SYSTEM.FOR TRANSMITTING SOUND QARRYING AND FIELD CURRENTS To REMOTELYLOCATED DYNAMIC LOUD SPEAKERS Filed June 14, 1930 '00 OTHER SELE TIVESWVI'CHING DEVICES Ioweniom v Patented Sept. 13, 1932 UNITED STATESPATENT OFFICE LAWRENCE O. PAINTER AND HOWARD L. JOHNSON, OF ST. PAUL,MINNESOTA, ASSIGNORS TO PROGRAM SERVICE COMPANY, OF ST. PAUL, MINNESOTASYSTEM FOR TRANSMITTING SOUND-CARRYING AND FIELD CURRENTS T BEMOTEL'YLOCATED DYNAMIC LOUD SPEAKERS Application filed June 14, 1930. SerialNo. 461,095.

This invention relates to transmission and distribution systems forsound programs, such as musical programs, addresses and the like andrelates particularly to systems wherein sound-carrying currents aretransmitted and distributed by conductors from a central station to anumber of distantly located dynamic loud speakers.

Such systems, while capable of wide general use, in the distribution ofsound programs, are especially well adapted for profitable, commercialuse by telephone companies. Telephone oflices or exchanges mayconstitute central stations, wherein several sources of sound-carryingcurrents may be amplified and these currents may be transmitted todistantly located dynamic loud speakers at the homes of the telephonesubscribers, thereby offering to said subscribers a selection of several programs.

At least one of the independent telephone companies in this country hasused a system of the general class above described, but up to this timewhere dynamic loud speakers are served by the system, it has been foundexpedient to employ amplifiers at the location of the dynamic speakersand it has been necessary to energize the field coils of said speakersfrom currents supplied from the amplifiers or from lighting or powersupply circuits available at the subscribers home or location of thespeakers, and in the latter instance, expensive apparatus, such asrectifiers, and transformers or batteries were required.

In addition to the substantial original expense of amplifiers for eachdynamic speaker, and/or the other'apparatus above described the same hadto be occasionally serviced an parts replaced by the company supplyingthe program entertainment to prevent the apparatus from losing itsefliciency and to insure roper volume at the subscribers home.

urthermore, the subscribers voften ob'ected to the increase in theirelectric light an power bills, because of current consumed in operatingthe amplifiers at their homes and/or in supplying currents forenergizing the field coils of the dynamic speakers.

It is an object of our invention to rovide a program transmission systemof t 0 class described, wherein remotely located dynamic speakers areutilized in connection with the system and wherein the saidobjectionable features of the systems heretofore used may a suppliedfrom the central station and simultaneously transmitted over the sameconductors.

It is a further object to provide a multiprogram system of the classabove described, wherein any one of a number of sources of sound carring current may be selected by a person at t e remote location of thedynamic oud speaker by means of a controlling circuit and a selectiveswitching device which is located at a point convenient to the centralstation and wherein the sound-carrying currents, the current forenergizing the field coil of the dynamic speaker and the current forremotely controlling the selective switch ing device are all transmittedfrom the central station by a single pair of conductors.

Another object is to provide a system of the type described, in thepreceding paragraph,

wherein a momentary operation 'of a device for changing the magnitude ofthe current flowing in the said controlling circuit for 0 rating theselective switching device will simultaneously effect the complete orpartial de-energization of the field coil of the dynamic speaker and theactuation of the selective switching device to connect a differentsource of sound-carrying current with the dynamic speaker.

These and other objects and advantages of the invention will be fullyset forth in the following description made in connection with theaccompanying drawing, wherein reference characters are applied to theseveral parts andwherein an embodiment of our system is diagrammaticallyshown, the elements and apparatus above the dotted line XX being locatedat the central station and g aevaoea the elements below said dotted linebeing located at a remote point, such as a subscribers home.

As schematically shown in the drawing, three different sources ofsound-carrying currents are available at the output terminals of threeamplifiers A A andA located at the central station. These amplifiers maybe secondary amplifiers of an amplifying system (not shown) and thesources of said sound-carryin currents may be derived from the outputs omicrophones, electrical phonogra hs or an other suitable source. Theamplifiers A 2 and A may serve a multiplicity of distantly locateddynamic speakers, as indicated in the drawing and for each dynamicspeaker or subscribers station a suitable selective switching device Bis provided, located at the central station or if desired at some pointconvenient to the central station and to a number of subscribers homes.The selective switching device utilized may be of any suitable typewhere a momentary change of the magnitude of a 25 controlling currentwill progress or step over the moving element of the switching evlce,

and wherein the momentary change in magnitude of said current may becontrolledat the distantly located loud speaker. An en- 30 tirelysatisfactory selective switching device is disclosed in our co-pendingapplication for U. Ei. Letters Patent entitled Selective multiprogramsystem for distribution of soundcarrying currents, S. N. 449,271, filedMay 2nd, 1930.

A pair of conductors 7 and 8 extend between the central station and thedistantly located dynamic speaker for transmitting sound-carryingcurrents and other currents necessary for operating the system, as willhereinafter be more fully set forth. These conductors may constitute aair of wires in a =::onv'entional telephone ca le.

The output terminals of amplifiers A A and A are connected with theconductors 7 and 8 through the contacts of the selective switchingdevice B and through condensers 2 and 3, said condensers preventing flowof direct current though the output trans 50 formers of the amplifiers.As illustrated, the

selective switching device includes a stepping magnet provided with theusual magnetic coils 5 and 6 and operating a spring actuated armaturebar Y which is equipped 55 with a pawl P engaging a ratchet R forprogressively rotating the selective switch control shaft S. A batteryor other source of direct current is connected to the conductors 7 and8, through the two stepping magnet coils and 6. The high reactance ofsaid magnet coils prevents the flow oi: audio frequency current throughthe batterv 1. In the type of tivc switching din illustrated, each illthe controlling circuit through the coils i tle eoergized or partiallyole-energized, the spring actuated armature bar Y will move from left toright causing a different source of sound-carrying current to beconnected with the conductors 7 and 8.

At the subscribers home or location of the dynamic speaker, which isindicated as an entirety by the letter E, a coupling transformer Cconsisting of three separate coils 9, lO'and 11 is wound on a singlecore D. One terminal of coil 9 is connected to conductor 7 and the otherterminal of coil 9 is connected to one terminal of a condenser 12. Theother terminal of condenser 12 is connected to one terminal of coil 11and the other terminal of coil 11 is connected to the conductor 8. Thetwo terminals of condenser 12 are also. connected respectively to thetwo terminals of the field coil 15 of a dynamic loud speaker E, and thecontacts of a key or push button 13 are connected in series with one ofthe conductors used in making the above described connection between thecondenser and field coil. The key or push button 13 is preferably of atype in which thecontacts are normally held in the closed position by aspring and open only momentarily while the key or push button isdepressed. The two terminals of the coil 10 of coupling transformer Care connected respectively to the two ends of the resistance element 14of a volume control potentiometer. One end of the above mentionedresistance element 14 and the movable contact 14a of the volume controlpotentiometer are connected respectively to the two terminals of thevoice coil 16 of dynamic speaker E.

Operation In operation, sound carrying current will follow a circuitstarting from one of the output terminals of one of the amplifiers A Aand A and continuing through the appropri ate connected contacts of theselective switching device 13 through condenser 2, conductor 7, throughcoil 9 of the coupling transformer at the location of the dynamicspeaker, through condenser 12, through coil 11 of the couplingtransformer and back to the amplifier through conductor 8, and theappropriate connected contacts of the selective switching device B.Sound carrying current tendint, to fiow through the condenser 12 at thesubscribers station or location of the dynamic speaker will not bediverted through the key 13 and field coil 15 due to the highinductive-reactance of said field coil. Audio frequency orsound-carrying current flowing in the coils 9 and 11 of couplingtransformer C, due to transformer action, will set up a substantiallysimilar sound carrying current flowing in the closed circuit, whichincludes the two terminals of the secondary coupling transformer coil10, this circuit being formed by the resistance element 14 of the volumecontrol. potentiometer and the conductors connecting the volume controlpotentiometer to the secondary winding 10 of the transformer.

Sound-carrying currentflowing in the resistance element 14 of the volumecontrol causes an audio frequency potential to exist between the twoends of the resistance element. All or a part of this potentialdepending upon the position of the movable contact 14a of thepotentiometer, is impressed upon a circuit comprising the voice coil 16of the dynamic loud speaker E and the sound-carrying current flowingthrough said voice .coil 16 of the dynamic speaker has substantially thesame wave formand characteristics as the sourd-carrying currentdelivered by the amplifier A. .The field coil of the dynamic speaker isenergized by direct current transmitted from the central station overthe cable pair of conductors 7 and Sin the following manner:

Current flows from the positive terminal of battery 4 and continuesthrough coil 6 of the stepping magnet through conductor 7 of the cablepair to the location of the speaker, through coil 9 of the couplingtransformer C through the contacts of key 13 to one end of the fieldcoil 15 and through the field coil and coil 11 ofthe couplingtransformer and back over the conductor 8 of the cable pair and throughcoil 5 of the stepping magnet, back to the negative terminal of battery4. It will be obvious that the direct current delivered to the fieldcoil 15 cannot be diverted through condenser 12 which is associated withthe coupling transformer C. It will also be obvious that the said directcurrent for energizing the field coil will have no effect upon thesound-carrying circuit fed from coil 10 of the coupling transformer.

In the embodiment of the invention illustrated, it will be seen that thefunction of the key or push button 13 is to momentarily interrupt whendepressed, the flow of direct current through the stepping magnet of theselective switching device, thereby causing the switching device to stepover to a new connection for connecting a different source ofsound-carrying current with the cable pair 7 and 8 and simultaneouslyde-energize the field coil 15 of the dynamic speaker, therebyeliminating at the location of the speaker, undesirable clicks or soundsduring the operation of the selective switching device. It will be seenthat with the type of selective device illustrated, when the enteringcircuit is opened or the magnitude of currents flowing thereinconsiderably reduced, the armature bar of the stepping magnet, due tothe spring, will move away from the magnet progressing the rotativeactuating element of the switching device one step.

It will further be seen that the coupling I transformer in combinationwith the connamely that of impedance matching transformer. Thetransformer windings" preferably have such a ratio that the impedanceloo ing into the primary of the coupling transformer C from the linewill be precisely that into which the amplifier is designed to operate.a

With our system, all sound-carrying currents and direct currents forenergizing the field coil and the dynamic speaker, as well as foroperating the selective switching device are conveniently supplied fromthe central station over a single pair of conductors, which convenientlymay be a cable pair disposed in a conventional communication cable.Amplifiers at the locations of the dynamic speakers are dispensed withand the necessity for lighting and power supply circuits at thesubscribers homes to energize the speaker and/or to control theselective switching mechanism, including the use of rectifiers,transformers or batteries 1' s obviated. The central ofiice or companysupplying the program service, with our system, furnishes all currentsfor operating the system and, the charge made to subscribers willinclude the entire subscribers expense, whereas formerly with dynamicspeakers at the subscribers home, the subscriber had to pay for thecurrent necessary to operate his amplifier and energize the field coilin addition to the service charges made by the company supplying theprogram service.

It will, of course, be understood that various changes may be made inthe form, details, arrangement and proportions of the parts withoutdeparting from the scone of our invention, which, generally stated,consists in a device capable. of carrying out the objects above setforth, in the novel parts and combinations of parts disclosed anddefined in the appended claims.

What is claimed is 2- 1. In a system for transm tting sound-carryingcurrent, a central station, a distantly located dynam c loud speakerhaving a. field coil and a voice coil, a number of sources ofsound-carrying currents available at said central station, amplifiersfor each of said sources of sound-carrying current, a selectiveuni-directionally progressive switching device located at a pointconvenient to said central'station and having a series of switchunitseach connected with one of said sources of sound-carrying current,a pair of conductors extending between said central station and saiddynamic loud speaker, a source of direct current at said central stationconnected with said conductors for supplying current for energizing thefield coil of said distantly located dynamic loud speaker, and for alsomagnetically operating said selective switching device, said same pairof conductors transmitting sound-carrying currents from said centralstation to said distantly located dynamic speaker,

2. In a system for transmitting sound-carrying current, a centralstation, a distantly located dynamic loud speaker having a field coiland a voice coil, a number of sources of sound-carrying currentsavailable at said central station, amplifiers for each of said sourcesof sound-carrying current, a selective uni-directionally progressiveswitching device located at a point convenient to said central stationand having a series of switch units each connected with one of saidsources of sound-carrying current, a pair of conductors extendingbetween said central station and said dynamic loud speaker, a source ofdirect current at said central station connected with said conductorsfor supplying current for energizing the field coil of said distantlylocated dynamic speaker and for also magnetically operating saidselective switching device, said same pair of conductors transmittingsound-carrying currents from said central station to said distantlylocated dynamic speaker, and means at the location of said dynamicspeaker for momentarily changing the magnitude of the controllingcurrent for said selective switching device and to simultaneously atleast partially de-ene-rgize said field coil of the dynamic speaker.

3. In a system for transmitting sound-carrying current, a centralstation having available a number of sources of sound-carrying currents,a distantly located dynamic loud speaker having a field coil and a voicecoil, :1 selective uni-directionally progressive switching devicelocated at a point convenient to said central station and having aseries of switch units each connected with one of said sources ofsound-carrying current, a pair of conductors extending between saidcentral station and said dynamic speaker, a source of direct currentavailable at said central station and connected with said conductors forsupplying current for energizing the field coil of said distant dynamicspeaker and for also magnetically operating said selective switchingdevice, said same pair of conductors transmitting sound-carryingcurrents from said sources to said distantly located dynamic speaker andmeans at the location of said dynamic speaker for momentarily changingthe magnitude of the controlling current for said selective switchingdevice.

4. In a system for transmitting sound-carrying current, a centralstation having available a number of sources of sound-carrying currents,a distantly located dynamic loud speaker having a field coil and a voicecoil,

an electro-magnetically operated selective switching device, the movingelement of which moves a predetermined distance each time the currentthrough the magnetic element is momentarily interrupted, said switchingdevice being located at a point c0nvenient to said central station andhaving a series of switch units each connected with one of said sourcesof sound-carrying current, a pair of conductors extending between saidcentral station and said dynamic speaker, a source of direct currentavailable at said central station and connected with said conductors forsupplying current for energizing the field coil of said distant dynamicspeaker and for also magnetically operating said selective switchingdevice, said same pair of conductors transmitting soundcarrying currentsfrom said sources to said distantly located dynamic speaker, and meansat the location of said dynamic speaker for momentarily interrupting thecontrolling current for said selective switching device.

In testimony whereof we afiiX our signatures.

LAWRENCE O. PAINTER. HOWARD L. JOHNSON.

